This intention relates to a method of preparing a plasma or serum sample from whole blood, especially to a method capable of obtaining a plasma or serum sample from whole blood having a high hematocrit value in a high separation rate without destroying blood cells.
Type or concentration of blood components, such as metabolites, proteins, lipids, electrolytes, enzymes, antigens, and antibodies, is measured, in general, using a plasma or serum sample obtained by centrifuging whole blood. However, centrifuging takes labor and time. Particularly, centrifuging is unsuitable for an urgent case of measuring a small number of samples promptly and in site inspection, because of requiring a centrifuge and electricity. Thereupon, it has been investigated to separate serum from whole blood by filtration.
Several filtration methods using glass fiber filter have been known wherein whole blood is charged into the glass fiber put in a column from one side of the column, and plasma or serum is obtained from the other side (Japanese Patent KOKOKU Nos. 44-14673, 5-52463, Japanese Patent KOKAI Nos. 2-208565, 4-208856)However, practical filtration methods capable of obtaining an amount of plasma or serum necessary for measuring by an automatic analyzer from whole blood have not been developed except a part of items, such as blood sugar.
The reason is seemed that previous filtration systems do not satisfy the following three conditions
1) It is difficult to obtain a sufficient amount of plasma necessary for automatic analysis by filtration. PA1 2) Erythrocytes tend to destroy (hemolyze) through filtration, and accordingly, it is difficult to measure analytical items which are liable to be affected by hemoglobins released into plasma or serum by hemolysis or analytical items wherein quantity in blood cells is greater than plasma or serum, such as GOT, GPT, LDH, Va and K. PA1 3) In the case of high hematocrit value (50% or more) samples, it is difficult to filter because of clogging filtering material by erythrocytes. PA1 (1) Not to destroy erythrocytes (hemolyze) in plasma separation When erythrocytes are destroyed, blood cell components of which quantity in blood cells is much greater than in plasma, such as Hb, GOT, LDH and K are released into plasma to cause analytical error. Hb released into plasma interferes with optical measurement. PA1 (2) Sure plasma separation even from whole bloods having a high hematocrit value (50% or more) with difficulty in erythrocyte separation, and having tendency to hemolysis. When hematocrit value rises, separation by filtration becomes difficult due to sharp increase of blood viscosity. PA1 (3) Variation of composition do not occur in plasma separation.
For example, Japanese Patent KOKOKU No. 6-64054 discloses plasma filtration technique by glass fiber filter made of a particular material, but it states that plasma amount capable of taking out shall be limited to 1/2 or less of the volume of glass fiber filter. In the Japanese patent, on the premise that hematocrit value is 50%, it is supposed that space of glass fiber filter is filled out by erythrocytes, and the quantity of plasma obtained by filtering up to the filled out state is set 50% of the volume of glass fiber filter at maximum However, whole blood samples having a hemotocrit value of 55 to 60% are not rare among whole blood samples daily dealt in clinical assay organization.